Trilobites of the Genus Megistaspis from the Vaginatum Limestone of Scandinavia

Eleven species of the asaphid genus Megistaspis Jaanusson are described from the Lower Ordovician Vaginatum limestone of Sweden and one species from the corresponding beds of the Oslo region, Norway. Five new species names are proposed. Megalaspis rudis Angelin is considered a nomen dubium, and the members of Megistaspis with a more or less smooth pygidium previously referred to this species are included in the new species M. convexa and M. bombifrons. The type material of M. grandis (Sars) is redescribed and considered to belong to a separate species hitherto known only from Norway. Examination of the types and additional material of M. heros (Dalman) has shown that the specimens from Öland, lngerman­land, and Estonia previously referred to this species belong to M. heroica n. sp. Similarly, the material from Ingermanland and Estonia described by F. Schmidt (1906) as Megalaspis acuti­cauda Angelin is considered here as a separate new species, M. spinulata, which seems to occur also in Öland together with M. acuticauda. Eight of the species described belong to the subgenus Megistaspis (Megistaspidella) Jaanusson, 1956, whereas M. heros, M. heroica, and M. lawrowi cannot at present be placed in any known subgenus of Megistaspis. A close examination of some well preserved pygidiahas revealed that the boundaries between the segments in Megistaspis run in front of the ribs, and not in the rib furrows.